1. Field of the Invention
The invention relates to a method for producing a unidirectional or “UD” layer with a predetermined layer width from a predetermined number of filament strands, in which the filament strands are spread out to form bands transversely to the longitudinal direction of the UD layer and arranged next to one another.
Furthermore, the invention relates to a device for producing a UD layer with a predetermined layer width with a filament strand dispenser arrangement from which a predetermined number of filament strands can be drawn off simultaneously, a spreading device for each filament strand to spread out the filament strand transversely to its longitudinal direction to form a band, and a bobbin carriage for jointly winding up the spread out bands arranged next to one another.
The invention is described below based on the example of filament strands with carbon filaments. However, it is not restricted to carbon filaments.
2. Discussion of Background Information
Carbon filaments are sold in filament strands that contain 12,000, 24,000, 48,000 or more carbon filaments. The larger the number of carbon filaments, the more cost-effective the filament strands are in general. The filament strands have in cross section approximately the shape of an ellipse or a circle.
So-called UD layers are often required in the production of fiber-reinforced plastics. In a UD layer the fibers or filaments all are present in the same main direction. Although they do not have to be aligned exactly parallel to one another, they all run in the same direction. A fiber-reinforced plastic then has an increased tensile strength in this direction.
In order to be able to produce a UD layer of this type from the filament strands, the filament strands have to be arranged next to one another and spread out to form bands. The bands then present next to one another in one plane are then wound up jointly or jointly processed in another manner. Under some circumstances a transverse cohesion is produced between adjacent bands.
If increased tensile strengths in several directions are desirable in the subsequent plastic product with reinforcing fibers, then several UD layers with different fiber directions are laid one on top of the other and then embedded jointly into a plastic.
A method and a device of the type referenced at the outset are known, for example, from EP 0 972 102 B1.
DE 10 2005 008 705 B3 shows a device for feeding fiber bands to a knitting machine, in which the fiber bands are drawn off from bobbins at a uniform speed, but are further processed with predetermined stoppage times. During the stoppage times the fiber bands are temporarily stored in a controlled storage means.
From DE 10 2005 052 660 B3 a device and a method are known for spreading out a carbon fiber hank. In order to be able to better spread out the fiber hank, it is heated by conducting an electric current through it.
DE 197 07 125 A1 describes a method for producing unidirectional scrims, in which the spread out fibers are connected to one another by transverse connecting threads in order to form a web.
The spreading out of the filament strands to form the bands is simply carried out in that the filament strands are drawn with a certain tension over a deflection device, for example, a round rod. Due to the tensile stress, all of the filaments or fibers have the tendency to approach the rod. Filaments or fibers that are arranged closer to the rod are thereby displaced laterally outwards by the filaments or fibers arranged further away. A spreading of the filament strand to form the bands is automatically produced hereby.
However, it can be observed that a UD layer that is produced with bands of this type has a certain waviness or unevenness, in other words an irregular thickness, transversely to its longitudinal extension.